Operation of fluid systems such as pumps, compressors, mixers, separators and other such systems submerged underwater is difficult because the operating environment is harsh, particularly if that environment is deep seawater. The water surrounding the system and often the process fluid flowing through the system is corrosive. The ambient environment can be cold, making many materials brittle and causing large thermal expansion/contraction of equipment as the equipment cycles between hot operating and cold not-operating states. The hydrostatic pressure of the water and/or process fluid can be substantial. Furthermore, installation and access to the fluid systems for maintenance and repair is difficult and expensive because the systems are often deployed in geographically remote locations and at depths inaccessible by divers, therefore requiring purpose-built vessels, skilled personnel and robotic equipment.